On Wed, Jan 14, 2015 at 03:22:25PM +0000, Petr Cermak wrote:
> On Wed, Jan 07, 2015 at 07:24:52PM +0200, Kirill A. Shutemov wrote:
> > And how it's not an ABI break?
> I don't think this is an ABI break because the current behaviour is not
> changed unless you write "5" to /proc/pid/clear_refs. If you do, you are
> explicitly requesting the new functionality.
I'm not sure if it should be considered ABI break or not. Just asking.
I would like to hear opinion from other people.
> > We have never-lowering VmHWM for 9+ years. How can you know that nobody
> > expects this behaviour?
> This is why we sent an RFC [1] several weeks ago. We expect this to be
> used mainly by performance-related tools (e.g. profilers) and from the
> comments in the code [2] VmHWM seems to be a best-effort counter. If this
> is strictly a no-go, I can only think of the following two alternatives:
>
> 1. Add an extra resettable field to /proc/pid/status (e.g.
> resettable_hiwater_rss). While this doesn't violate the current
> definition of VmHWM, it adds an extra line to /proc/pid/status,
> which I think is a much bigger issue.
I don't think extra line is bigger issue. Sane applications would look for
a key, not line number. We do add lines there. I've posted patch which
adds one more just today ;)
> 2. Introduce a new proc fs file to task_mmu (e.g.
> /proc/pid/profiler_stats), but this feels like overengineering.
>
> > And why do you reset hiwater_rss, but not hiwater_vm?
> This is a good point. Should we reset both using the same flag, or
> introduce a new one ("6")?
>
> [1] lkml.iu.edu/hypermail/linux/kernel/1412.1/01877.html
> [2] task_mmu.c:32: "... such snapshots can always be inconsistent."
--
Kirill A. Shutemov
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